We're searching for life, Jim, but not as we know it

Some of the world's top space boffins have proposed a new way to figure out the odds of finding life - but not as we know it - on another planet.

The brainy bunch, composed of scientists from NASA, SETI, the German Aerospace Centre and four universities, suggested that so far our search for life in the universe has concentrated too much on finding planets similar to our home world. While it is logical to try to find another Earth, because it's likely that it will be populated in some way, the researchers said we should look for other conditions that might support life.

"The first question is whether Earth-like conditions can be found on other worlds, since we know empirically that those conditions could harbour life," Dr Dirk Schulze-Makuch, astrobiologist at Washington State University, said. "The second question is whether conditions exist on exoplanets that suggest the possibility of other forms of life, whether known to us or not."

In a paper to be published in next months's Astrobiology, the team said that the search of planets outside our solar system should first use an Earth Similarity Index and then look at a Planetary Habitability Index "for describing a variety of chemical and physical parameters that are theoretically conducive to life in more extreme conditions".

"Habitability in a wider sense is not necessarily restricted to water as a solvent or to a planet circling a star," the paper's authors write.

"For example, the hydrocarbon lakes on Titan could host a different form of life. Analog studies in hydrocarbon environments on Earth, in fact, clearly indicate that these environments are habitable in principle. Orphan planets wandering free of any central star could likewise conceivably feature conditions suitable for some form of life."

The boffins admit that this is something a bit like imagining all possible sorts of life forms and searching for them, or to put it in more scientific wording "an intrinsically more speculative endeavour". However, they argue that not doing it risks overlooking potentially habitable worlds. ®